Boosting the efficiency of Smith-Purcell radiators using nanophotonic inverse design

TL;DR

This paper demonstrates that nanophotonic inverse design significantly enhances the efficiency and control of Smith-Purcell radiation sources, enabling more practical and tunable free-electron radiators.

Contribution

The study introduces the application of nanophotonic inverse design to optimize Smith-Purcell radiators, achieving higher efficiency and spectral shaping capabilities.

Findings

Radiator efficiency increased by 3 times compared to traditional designs.

Overall power output was improved by 2.2 times.

Simulations indicate potential 96-fold efficiency improvement with better fabrication.

Abstract

The generation of radiation from free electrons passing a grating, known as Smith-Purcell radiation, finds various applications including non-destructive beam diagnostics and tunable light sources, ranging from terahertz towards X-rays. So far, the gratings used for this purpose have been designed manually, based on human intuition and simple geometric shapes. Here we apply the computer-based technique of nanophotonic inverse design to build a 1400nm Smith-Purcell radiator for sub-relativistic 30 keV electrons. We demonstrate that the resulting silicon nanostructure radiates with a 3-times-higher efficiency and 2.2-times-higher overall power than previously used rectangular gratings. With better fabrication accuracy and for the same electron-structure distance, simulations suggest a superiority by a factor of 96 in peak efficiency. While increasing the efficiency is a key step needed for practical applications of free-electron radiators, inverse design also allows to shape the spectral and spatial emission in ways inaccessible with the human mind.